In recent years, with the progress of information-oriented society several types of identification (ID card) cards have come into use. For instance, cards involved in the electronic transfer of money include bank cards, pay cards, credit cards and shopping cards. Different types of security cards authorize access to the bearer of the card to particular areas such as a company (employee ID card), the military, a public service, the safe department of a bank, etc. For long time national states have issued identity cards to establish the national identity of their civilians. Still other types of identification cards include social security cards, membership cards of clubs and societies, and driver's licence cards. Such ID cards usually contain information referring both to the authority issuing the card on the one hand and to the owner of the card. The first type of information may be general information such as a name and/or logo of the issuing authority, or security marks, such as a watermark and security print, e.g. a repeating monochrome pattern or a gradually changing colour pattern which are difficult to counterfeit. The second type includes e.g. the unique card number, personal data such as a birth day, a photo of the owner, and a signature. The card can further contain hidden information and therefore contain a magnetic strip or an electronic chip (“smart cards”).
A large set of ID cards are usually prepared on a large carrier of information such as a web or sheet by a step and repeat process, after which the information carrier is cut into multiple items with the appropriate dimensions each representing a personal ID card. Smart cards and ID cards have now the standardized dimensions of 85.6 mm×54.0 mm×0.76 mm.
Normally, the card is protected by a plastic sheet material such as by lamination of the card to a plastic sheet or, as it is usually the case by lamination between two plastic sheets.
In view of their widespread uses, especially in commercial transactions, such as cashing checks, credit purchases, etc., it is important that the person relying on the ID card to identify the bearer have maximum assurance that the ID card has not been altered and/or that the ID card is not a counterfeit. A great deal of ingenuity has been employed to provide this desired degree of assurance. For example, specialized adhesive systems and lamination techniques have been developed to prevent or discourage alteration of ID cards. These systems and techniques are designed to achieve a high degree of bonding efficiency between a surface of the card and any plastic sheet material bonded to it. Certain adhesive systems, for example, can provide what is known in the art as a “security seal”. A “security seal” is best explained by describing what happens if an attempt is made to pull a plastic sheet material from the surface of a card bonded to the plastic. If a “security seal” exists, all or at least portions of the adhered surface will be removed from the card together with the plastic sheet material. Accordingly, a “security seal” is normally established between the information-bearing surface of the card or document and the plastic. Under such circumstances, removal of the plastic should also remove substantial portions of the information-bearing surface of the card to render the card unusable for alteration purposes. Adhesives or adhesive systems which can provide “security seals” are described in e.g. U.S. Pat. Nos. 3,582,439, 3,614,839 and 4,115,618. According to U.S. Pat. No. 4,322,461 a security seal can be provided by applying heat-sealable polymers so as to obtain a sealed envelop-type pouch.
Furthermore, the art's response to the counterfeiting problem has involved the integration of “verification features” with ID cards to evidence their authenticity. The best known of these “verification features” involve signatures such as the signature of the person authorized to issue the ID card or the signature of the bearer. Other “verification features” have involved the use of watermarks, fluorescent materials, validation patterns or markings and polarizing stripes among others. These “verification features” are integrated into ID cards in various ways and they may be “visible” or “invisible” in the finished card. If “invisible”, they can be detected by viewing the feature under conditions which render it visible. Details relating to the use of “verification features” in ID cards can be found, for example: U.S. Pat. Nos. 2,984,030; 3,279,826; 3,332,775; 3,414,998; 3,675,948; 3,827,726 and 3,961,956.
The present invention extends the teaching on verification marks, and particularly on watermarks.